Waterpipe tobacco smoking (WTS) is increasing in the U.S. among young adults exposing them to its many health risks. This increase is partly to due to waterpipe tobacco product and social allure ads that manufacturers, waterpipe bars and cafs use to portray WTS as a fun, social activity while masking its harmful effects. The positive feelings these ads likely elicit may reduce worry and perceived health risks and increase the appeal of WTS. Ad appeal may be curbed by placing health warnings. Thus, we address the extent to which the addition of text only and text + graphic (i.e., pictorial) health warnings influence reactions to waterpipe tobacco ads as well as risk appraisals, attitudes toward WTS, and intention to engage in WTS. This research will be carried out in three phases involving young adults ages 18-34 who engage in WTS at least monthly or who are susceptible to use. Phase 1 and 2 will use the crowdsourcing data collection platform Turkprime. In Phase 1, with panels of waterpipe tobacco users and susceptible nonusers, we will create and refine WTS health warnings in four domains: 1) longer-term health effects, 2) shorter-term health effects, 3) addictiveness, and 4) types and levels of toxicant exposures; and select the most appealing product and social allure ads. The most promising text/graphic warnings in each domain and the most appealing product and social ads will be tested in Phase 2. In Phase 2, waterpipe users and susceptible nonusers will be randomized to view product or social allure ads without or with health warnings (text only or text + graphics) covering the four health domains. Reactions to ads will include attitudes toward each ad and ad appeal to engage in WTS. In addition, main outcomes will include risk appraisals (e.g., perceived risk and worry about harms), attitudes toward WTS, and intention to quit/willingness to try WTS. As a two-week follow-up, we will reassess these outcomes, WTS behavior and recall of ad content. In Phase 3, we will conduct an eye-tracking study to assess how attentional processes mediate reactions the health warnings. The primary aims are: 1) develop, pilot test and select health warnings in four domains as well as product and social allure ads to be used in (Phase 2); 2) explore whether reactions to ads as well as risk appraisals, attitudes toward WTS, and intentions to engage WTS vary by ads with or without health warnings; 3) explore whether effects of warnings on risk appraisals, attitudes toward WTS, and intention to engage in WTS are mediated by reactions to the ads; and 4) examine how attentional processes as assessed using eye-tracking mediate reactions to health warnings. Findings will inform messaging strategies to curb WTS and potentially the FDA?s regulation of WTS ads.